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Search: id:A000060
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| A000060 |
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Number of signed trees with n nodes.
(Formerly M0904 N0340)
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+0
2
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| 1, 2, 3, 10, 27, 98, 350, 1402, 5743, 24742, 108968, 492638, 2266502, 10600510, 50235931, 240882152, 1166732814, 5702046382, 28088787314, 139355139206, 695808554300, 3494391117164, 17641695461662, 89495028762682, 456009893224285, 2332997356507678, 11980753878699716, 61739654456234062, 319188605907760846
(list; graph; listen)
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OFFSET
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1,2
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
F. Harary and G. Prins, The number of homeomorphically irreducible trees and other species, Acta Math., 101 (1959), 141-162.
P. Leroux and B. Miloudi, ``G\'{e}n\'{e}ralisations de la formule d'Otter,'' Ann. Sci. Math. Qu\'{e}bec, Vol. 16, No. 1, pp. 53-80, 1992.
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..500
F. Harary and G. Prins, The number of homeomorphically irreducible trees and other species, Acta Math., 101 (1959), 141-162.
P. Leroux and B. Miloudi, Generalisations de la formule d'Otter, Ann. Sci. Math. Quebec 16 (1992), no 1, 53-80.
Index entries for sequences related to trees
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FORMULA
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Generating function A(x) is such that A(x)=S(x)+S(x^2)-S(x)^2, where S(x) is the generating function for A000151 - Pab Ter (pabrlos2(AT)yahoo.com), Oct 12 2005
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MAPLE
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unassign('x'): with(combstruct): norootree:=[S, {B = Set(S), S = Prod(Z, B, B)}, unlabeled]: S:=x->add(count(norootree, size=i)*x^i, i=1..30): seq(coeff(S(x)+S(x^2)-S(x)^2, x, i), i=1..29); # with Algolib (Pab Ter)
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CROSSREFS
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Adjacent sequences: A000057 A000058 A000059 this_sequence A000061 A000062 A000063
Sequence in context: A052929 A151415 A134588 this_sequence A089752 A007029 A099435
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KEYWORD
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nonn,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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More terms from Pab Ter (pabrlos2(AT)yahoo.com), Oct 12 2005
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